This is how to seal a wood gutter joint, with highly elastic tri-polymer sealant made by geocel that can be purchased online here.. I'm installing some fir gutters and am intent on sealing the end grain well on the joints. the joints consist of mitered returns on the ends and 45 degree scarf. Leaking gutter joints. a complete guide to diagnosing and then repairing leaking joints on metal, cast iron and plastic gutters..
